I have a Hennessey
Ultralight Expedition A-Sym and though I like the Hennessey Hammocks very
much I have struggled
with keeping my back warm in cool weather.
I searched for a workable underquilt, but couldn’t find one, and after
reading Ed Speer’s book Hammock Camping I decided to make one. It
turned out to be more challenging than I had anticipated, partly because
of its
odd shape and partly because I had to make allowances for moving around
while I
sleep.

Here
is one solution that works well. It makes the HH very warm, placing 1” of
down below areas of the hammock that are overlapped with a sleeping quilt (I
use a quilt similar to the Back country blanket) and 1 ½” of
down beneath the back and kidneys where the extra insulation is needed.
We are experiencing
mid winter here, so it will be a while before I can test the quilt for
condensation, but care was taken to make it breathable yet wind resistant,
so condensation
may be eliminated. Though I did not intend the quilt for winter use I
will use it this winter.

The pattern was made filling the hammock to establish it’s “occupied” shape,
then clipping cotton fabric to the outside of the hammock with binder clips
and gathering parts of the fabric until a fit was established. Initially a
channel was made in this pattern for a shock cord to pass between the hammock “pull-out
points to keep the quilt snug against the underside of the hammock but
as the design progressed the shock cord was replaced with 5/8 inch elastic..

There is a lot of shaping involved to make it fit the exterior of the hammock.
In the photo below, the foot end is on the left, and two large darts give it
a distinct bathtub shape at the foot. A single dart shapes the head end. The
quilt is not slit for entry/exit as the hammock is. The foot end of the hammock
is somewhat shorter than the head end, and with longer shock cord it is a simple
matter to move the quilt out of the way for entry and exit, and the quilt then
snaps back in to position to cover the entry slot

The
inside of the quilt (I will call it the “liner”) is of un-coated
1.1 oz rip-stop nylon and carries the load structurally. Elastic on all
edges and across the bottom (tie-out to tie-out) to hold it gently against
outside
of hammock, and the suspension points are attached and gusseted to this
fabric. Note that the elastic across the bottom is carried in a pocket sewn
to the
liner to allow it to stretch and move without interfering with the down,
and the baffles are not stitched through this elastic. The light colour of
this
liner was chosen because it is more reflective than a darker colour.

The transverse baffles are made of NoSeeUm mesh at 5” intervals, cut
on a radius to allow for the differential between the liner and the outside
shell. I noted on my pattern the area in the hammock where I normally slept
(diagonal in accordance with the asymmetrical nature of the hammock) and increased
the thickness of the down in those areas that are normally beneath my head,
back (particularly kidneys) and legs, and thinned the fill in areas above my
head, below my feet, and in the sides – so, in the thinner areas the
down thickness is approx. 1” and below my back and kidneys the thickness
increases to slightly over 1 ½ “. That is substantial considering
that it is below me, but it eliminates unnecessary bulk of insulation in
areas where it is not needed. I filled it with some amazing 800+ fill down
and even
allowing a 20% overfill the quilt only required 4.41 oz (125.10 grams)
to fill it. Down was weighed on an old Chemistry lab scale to +/- 1/10
gram
per baffle,
which sounds overly careful, but the smallest baffle at one of the ends
required less than 3 grams (the weight of a penny) and so errors larger
than 1/10th
gram could be visible.

The outside shell of the quilt is 1.1 oz. rip-stop with a DWR (Durable Water
Resistant) treatment to protect the down from rain-splash etc. It is larger
than the liner due to the differential caused by the outside radius, and
care was taken to assure that at all points the reinforced liner carried any
stress.
The exposed stitching from the baffles and around the edges were sealed
with Revivex (a durable water resistant/breathable treatment marketed by GoreTex)
applied with a Q-tip.

The
toggles are attached to the elastic, which is folded over and secured along
with the gusset on the liner (blue)
The quilt attaches to the hammock on the ends with 3/16 “ shock cord
with 1 “ toggles made of ¼ “ dowel that slip beneath
key rings at the hammock ends. The side attachments are 1 ¼” dowel
toggles attached to the elastic (doubled over and fed back and attached
to the gusset on the liner)

The quilt attaches to the hammock on the ends with 3/16 “ shock cord
with 1” toggles of ¼ “ dowel that slip beneath key rings
at the hammock ends. Note that grosgrain guide loops are added to the hammock
edges maintain the shape of the quilt and keep it snugly against the hammock,
but the shock cords attach at the hammock ends, so little stress is placed
on the hammock itself. The side attachments are somewhat larger dowel toggles
attached to the elastic (doubled over and fed back and attached to the
gusset on the liner)

The total weight of the quilt, including shock cord and toggle attachments
included is 10.86 oz. (308 grams)

Because of the low volume of both the shell and the down fill, the snakeskins
supplied with the hammock will encase the hammock with the quilt attached,
but without the fly, which I carry separately in the outside mesh pocket of
a modified G-4. They are, however, quite snug and compress the down more than
I wish, so I will consider making a set of snakeskins with a 25% greater diameter,
the quilt attaches so quickly, however, that the new snakeskins are not really
necessary.